The present invention generally relates to semiconductor devices and more particularly to monitoring capacitance changes in deep trench (DT) capacitors using X-ray diffraction (XRD) measurements.
Deep trenches may be used in the semiconductor industry to provide a variety of useful devices including deep trench (DT) capacitors. The deep trenches may be formed in the semiconductor substrate and may typically include a depth exceeding 1 micrometer, or 1 micron, in contrast to shallow trenches having a depth less than 1 micron. The deep trenches may be generally utilized in a stand-alone semiconductor circuit such as a dynamic random access memory (DRAM) circuit to provide DT capacitors.
Typically, DT capacitors are formed in the semiconductor substrate (e.g. silicon wafer) using one or more conventional techniques, such as reactive ion etching (RIE), with photoresist or other materials as a mask to cover the areas where trench formation may not be desired. The deep trench may be typically filled with a conductor material (most commonly n-type doped polysilicon), which may serve as one plate of the capacitor, usually referred to as the “storage node.” The second plate of the capacitor may be typically formed by out diffusion of an n-type doped region surrounding the lower portion of the trench, usually referred to as the “buried plate.” A node dielectric layer, which may include, for example, silicon dioxide (SiO2), silicon nitride (SiN), silicon oxynitride (SiON), tantalum oxide (Ta2O5), aluminum oxide (Al2O3), or any other dielectric material, may be provided to separate the storage node and buried plate, thereby forming the DT capacitor. Field effect transistor (FET) devices may be formed in the semiconductor substrate adjacent to the DT capacitors. The capacitance value of the deep trench may depend on the size of the deep trench area. Typically, the deeper the deep trench, the larger the capacitance value.
Deep trench parameters such as volume and surface area may have significant impact on the DT capacitor characteristics including capacitance, resistance, and leakage current. Typical approaches for assessing DT trench capacitors may include destructive and nondestructive electrical testing. The capacitance of the deep trench may be one of the most important parameters for trench DRAM, embedded DRAM, application specific integrated circuits (ASICs), and system-on-chip products. By knowing the deep trench capacitance, evaluation of process integrity and prediction of device parameters may be conducted for process optimization. However, in current semiconductor fabrication technology, deep trench capacitance may be directly measured only after wafers reach the end of the process.